Powder pressing apparatus and powder pressing method

ABSTRACT

A powder pressing apparatus comprises an upper punch and a lower punch for compression of a powder in a cavity formed in a through hole of a die. A gap between a side surface of the lower punch and a side surface of the through hole of the die is sealed by a sealing member. A lubricant is supplied with a gas from a nozzle in the side surface of the lower punch to the side surface of the through hole, and the lubricant applied to the side surface of the through hole is spread by an absorbing member. The cavity is filled with the powder while the cavity is under suction by a reduced pressure provided from the nozzle in the side surface of the lower punch. During the suction, a filtering member provides filtration for the lower punch not to draw the powder in.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a powder pressing apparatus anda powder pressing method, and more specifically to a powder pressingapparatus and a powder pressing method for formation of a green compactby compressing a rare-earth magnetic powder filled in a cavity.

[0003] 2. Description of the Related Art

[0004] Generally, a rare-earth magnetic powder pressing apparatus of theabove kind comprises a die having a vertical through hole, an upperpunch to be inserted from above the through hole of the die, and a lowerpunch inserted into the through hole of the die for sliding movementrelative to the die. The lower punch provides a cavity within thethrough hole of the die. The cavity is filled with the rare-earthmagnetic powder gravitationally supplied from above and then, the upperpunch is inserted into the through hole so that the rare-earth magneticpowder is pressed by the upper punch and the lower punch into a compact.

[0005] According to the above pressing apparatus, generally, a lubricant(mold releasing agent) is applied to a side surface of the through holefor prevention of seizure of the side surface of the through hole aswell as for ease of removing the compact out of the through hole. Forthis particular operation, there is an apparatus disclosed in JapanesePatent Laid-Open No. 3-291307, in which a nozzle is provided on a sidesurface of the lower punch. According to this apparatus, while the dieis moving relative to the lower punch, the lubricant is supplied to theside surface of the through hole directly from the nozzle, therebyimproving operating efficiency of the apparatus.

[0006] On the other hand, Japanese Utility Model Laid-Open 62-146597discloses an apparatus in which a suction port is provided in the sidesurface of the through hole of the die or in a lower surface of theupper punch. When the powder is pressed into the compact, air and othergases within the cavity are sucked (deaerated), thereby decreasing theamount of the gases captured in the compact.

[0007] There are problems, however. According to the former disclosure(Japanese Patent Laid-Open No. 3-291307), although the lubricant can beapplied reliably to a region of the side surface of the through hole ofthe die near the nozzle, it is difficult to make the applicationuniformly to the entire side surface of the through hole. As a result,it becomes difficult to reliably remove the compact from the throughhole. If the application is to be made uniformly, on the other hand,then a large amount of the lubricant must be supplied, so that thecompact is coated with an unnecessary amount of the lubricant. Theexcess amount of the lubricant will make a surface of the compactbrittle, and therefore susceptible to a cracking or a flaking defect.Further, if the former conventional apparatus is used to press therare-earth magnetic powder, the lubricant, which is an organic compound,is likely to increase carbon content of the compound after sintering,deteriorating magnetic characteristics of a rare-earth magnet.Furthermore the green compact comprised of the powder manufactured by astrip casting process has a poorer compact strength due to a sharpdistribution curve of grain sizes.

[0008] According to the above pressing apparatus, the cavity is filledwith the rare-earth magnetic powder gravitationally supplied from above.This often causes the powder to be filled un-uniformly, particularly ata corner portion formed by the side surface of the through hole of thedie and the lower punch. This problem is especially serious if thepowder being used is manufactured by a strip casting process, becausethe powder made by the strip casting process has a much poorer fluiditythan mold casting process, characterized by a sharp distribution curveof grain sizes. Thus, an attempt may be made to apply the latterapparatus (Japanese Utility Model Laid-Open No. 62-146597) for makingsuction from the side surface of the through hole of the die while thepowder is being filled into the cavity.

[0009] However, although the provision of suction port in the sidesurface of the through hole of the die makes possible to deaerate, it isdifficult to form a large number of suction ports uniformly. Further,even if the suction is performed from the side surface of the throughhole of the die, it is still difficult to improve uniformity of thepowder filling, particularly at the corner portion formed by the lowerpunch and the side surface of the through hole of the die. Therefore,improvement is not achieved in quality or yield of the compact. As aresult, improvement is not achieved in productivity, either.

SUMMARY OF THE INVENTION

[0010] It is therefore a primary object of the present invention toprovide a powder pressing apparatus and a powder pressing method capableof improving the quality and yield of the compact, thereby improving theproductivity.

[0011] According to an aspect of the present invention, there isprovided a powder pressing apparatus for formation of a compact bypressing a powder, comprising: a die having a vertical through hole; afirst punch and a second punch, each being vertically movable within thethrough hole relative to the die, for compression of the powder within acavity formed in the through hole; and a supplying means including asupply port provided in a side surface of the first punch, for supply ofa lubricant with a gas from the supply port to the side surface of thethrough hole within the through hole.

[0012] According to another aspect of the present invention, there isprovided a method of pressing a powder for formation of a compactthrough compression of the powder by a first punch and a second punchwithin a cavity formed in a vertical through hole of a die, comprising:a lubricant supplying step of supplying a lubricant with a gas from aside surface of the first punch to a side surface of the through holewithin the through hole; a powder filling step of filling the cavitywith the powder; and a press forming step of forming the compact bypressing the powder filled in the cavity by the first punch and thesecond punch.

[0013] According to the present invention, a lubricant with a gas issupplied in a form of a spray or mist for example, from a side surfaceof the first punch to a side surface of the through hole of the die.Therefore, the lubricant can be applied easily and uniformly to the sidesurface of the through hole of the die, applying only a relatively smallamount of the lubricant. As a result, the compact can be reliably takenout of the through hole. Further, magnetic characteristics of a magnetobtained by sintering the compact can be improved since carbon contentof the resulting magnet is small. As a result, it becomes possible toimprove the quality and yield of the compact, thereby improving theproductivity.

[0014] According to the present invention, preferably, the lubricantapplied to the side surface of the through hole is spread by anabsorbing member for example. This makes possible to apply the lubricanteven more uniformly on the side surface of the through hole, makingpossible to provide more saving of the amount of application.

[0015] Further, preferably, the first punch is formed to have apolyangular section so as to have an angular portion, and the lubricantis supplied from inside the first punch through near the angled portionto the side surface of the through hole. If the first punch is formed tohave a polyangular section, a corner portion of the through holecorresponding to the angled portion becomes susceptible to un-uniformapplication. However, by supplying the lubricant from near the angledportion of the first punch, it becomes possible to reliably apply thelubricant to the corner portion of the through hole. As a result, thecompact can be reliably taken out of the through hole of the die even ifthe first punch has the polyangular section, making possible to improvefurther the quality and yield of the compact, thereby improving theproductivity, as well as expanding life of the metal molds.

[0016] Further, preferably, the lubricant is supplied to the sidesurface of the through hole, while a gap between the side surface of thefirst punch and the side surface of the through hole is sealed by asealing portion for example provided in the side surface of the firstpunch farther away from the cavity than is the supply port. If the firstpunch is a lower punch, the lubricant is reliably discharged upward bythe sealing provided at the lower. portion of the supply port. As aresult, a body of powder captured between the side surface of the lowerpunch and the side surface of the through hole of the die can be removedby the upward blast provided by the lubricant with gas. Therefore, itbecomes possible to reduce wear on the side surface of the lower punchand the side surface of the through hole of the die caused by thepowder. This advantage becomes especially significant if the powdercontains a highly abrasive rare-earth magnetic powder. Further, theapplied lubricant can be prevented from flowing downward. On the otherhand, if the first punch is an upper punch, the lubricant can bereliably discharged downward by sealing an upper portion of the supplyport, and the applied lubricant can be preventing from leaking through agap between the upper punch and the side surface of the through hole tothe upper surface of the die and so on.

[0017] Further, preferably, the first punch is the lower punch. Asdescribed above, according to the present invention, the lubricant canbe applied easily and uniformly to the side surface of the through holeof the die, by using relatively small amount of the lubricant. As aresult, there is a very rare possibility for the lubricant to pool onthe upper surface of the lower punch. Thus, the powder is easily setinto form when pressed, and therefore the compact having desiredcharacteristics can be obtained. Even if the lower punch has the uppersurface formed into a recess, there is still a very rare possibility forthe lubricant to pool on the upper surface of the lower punch, andtherefore the same advantage is achieved.

[0018] Further, preferably, the powder contains a rare-earth magneticpowder. According to the present invention, application of anunnecessarily large amount of the lubricant to the compact can beprevented. Thus, even if the compact is formed from the powdercontaining the rare-earth magnetic powder, and if this compact issintered, a resulting rare-earth magnet has a low carbon content. As aresult, magnetic characteristics of the rare-earth magnet can beimproved.

[0019] According to another aspect of the present invention, there isprovided a powder pressing apparatus for formation of a compact bypressing a powder, comprising: a die having a vertical through hole; anupper punch and a lower punch, each being vertically movable within thethrough hole relative to the die, for compression of the powder within acavity formed in the through hole; and a sucking means including asuction port provided in a side surface of the lower punch, forproviding suction from the cavity under a reduced pressure from thesuction port while the cavity is being filled with the powder.

[0020] According to still another aspect of the present invention, thereis provided a method of pressing a powder for formation of a compactthrough compression of the powder by an upper punch and a lower punchwithin a cavity formed in a vertical through hole of a die, comprising:a powder filling step of filling the cavity with the powder while thecavity is under suction by a reduced pressure provided from a sidesurface of the lower punch; and a press forming step of forming thecompact by pressing the powder filled in the cavity by the upper punchand the lower punch.

[0021] According to the present invention, the cavity is filled with thepowder while the cavity is under suction by a reduced pressure providedfrom the side surface of the lower punch. Thus, the powder can bereliably filled even to the corner portion formed by the side surface ofthe through hole of the die and the lower punch, making possible toprevent un-uniform filling of the powder in the cavity. Thus, it becomespossible to improve the quality and yield of the compact, therebyimproving the productivity.

[0022] According to the present invention, preferably, filtration isprovided by a filtering member provided in the side surface of the lowerpunch for covering the sucking port for example, during the suction fromthe cavity by a reduced pressure for preventing the lower punch fromsucking the powder. This prevents clogging of the suction port, makingpossible to provide the suction reliably and uniformly.

[0023] Further, preferably, the lower punch is formed to have apolyangular portion so as to have an angled portion, and the cavity issucked by a reduced pressure provided from near the angled portion. Ifthe lower punch is formed to have a polyangular section, a cornerportion of the through hole corresponding to the angled portion becomessusceptible to un-uniform filling. However, through providing thesuction of the cavity by the reduced pressure from near the angledportion of the lower punch, such a corner portion can also be filledreliably with the powder, making possible to prevent un-uniform fillingreliably. As a result, it becomes possible to further improve thequality and yield of the compact, thereby improving the productivity.

[0024] Still further, preferably, the gap between the side surface ofthe lower punch and the side surface of the through hole of the die issealed by a sealing portion provided in the side surface of the lowerpunch below the suction port for example, while the cavity is under thesuction provided by the reduced pressure. This makes possible togenerate a partial vacuum above the lower punch while the cavity isunder suction, thereby improving effect of the suction.

[0025] As has been described here above, un-uniform filling of thepowder within the cavity is prevented. Thus, even if the powder includesa rare-earth magnetic powder having a poor fluidity, it becomes possibleto fill the corner portion of the through hole with the powder, makingpossible to form the compact of a good quality. Therefore, the presentinvention is effective if the powder includes the rare-earth magneticpowder. The present invention is specially effective if the rare-earthmagnetic powder is manufactured by a strip casting process, thus havinga poorer fluidity.

[0026] According to another aspect of the present invention, there isprovided a powder pressing apparatus for formation of a compact bypressing a powder, comprising: a die having a vertical through hole; afirst punch and a second punch, each being vertically movable within thethrough hole relative to the die, for compression of the powder within acavity formed in the through hole; a lubricant holding means provided ina side surface of the first punch, for application of a lubricant to aside surface of the through hole in contact with the side surface of thethrough hole,; and a lubricant supplying means for supply of thelubricant to the lubricant holding means.

[0027] According to still another aspect of the present invention, thereis provided a method of pressing a powder for formation of a compactthrough compression of the powder by a first punch and a second punchwithin a cavity formed in a vertical through hole of a die, comprising:a lubricant supplying step of supplying a lubricant to a side surface ofthe through hole by bringing a lubricant holding means holding thelubricant into contact with the side surface of the through hole; apowder filling step of filling the cavity with the powder; and a pressforming step of forming the compact by pressing the powder filled in thecavity by the first punch and the second punch.

[0028] According to the present invention, the lubricant can be appliedeasily and uniformly to the side surface of the through hole of the die,applying only a relatively small amount of the lubricant. As a result,the compact can be reliably taken out of the through hole. Further,magnetic characteristics of a magnet obtained by sintering the compactcan be improved since carbon content of the resulting magnet is small.As a result, it becomes possible to improve the quality and yield of thecompact, thereby improving the productivity.

[0029] Further, preferably, the powder contains a rare-earth magneticpowder. According to the present invention, application of anunnecessarily large amount of the lubricant to the compact can beprevented. Thus, even if the compact is formed from the powdercontaining the rare-earth magnetic powder, and if this compact issintered, a resulting rare-earth magnet has a low carbon content. As aresult, magnetic characteristics of the rare-earth magnet can beimproved.

[0030] The above described objects and other objects, features, aspectsand advantages of the present invention will become more apparent fromthe following detailed description of embodiments when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a schematic diagram of a rare-earth magnetic powderpressing apparatus as an embodiment of the present invention;

[0032]FIG. 2 is a perspective view showing a lower punch;

[0033]FIG. 3 is an exploded perspective view showing an internalconstitution of the lower punch;

[0034]FIG. 4 is a sectional view showing a horizontal section of a ringportion of the lower punch;

[0035]FIG. 5 is a diagram showing a sequence of operation of therare-earth magnetic powder pressing apparatus;

[0036]FIG. 6 is a diagram showing a sequence of operation of therare-earth magnetic powder pressing apparatus if suction is not providedwhile the powder is being filled; and

[0037]FIG. 7 is a perspective view showing a variation of the lowerpunch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] An embodiment of the present invention will be described herebelow with reference to the attached drawings.

[0039] Referring now to FIG. 1, a rare-earth magnetic powder pressingapparatus 10 as an embodiment of the present invention comprises a die14 provided with a vertical through hole 12 having a rectangularsection, an upper punch 16 for insertion into the through hole 12 of thedie 14 from above, and a lower punch 18 inserted in the through hole 12of the die 14. The lower punch 18 is fixed to a main body 20 of thepressing apparatus. On the other hand, the die 14 is movable in verticalreciprocation by an unillustrated electric motor or cylinder forexample, so that the lower punch 18 is vertically movable relative tothe die 14. As shown in FIG. 1, when the die 14 is raised relative tothe lower punch 18, a cavity 22 is formed by the lower punch 18 in thethrough hole 12 of the die 14.

[0040] The die 14 has an upper face provided with a feeder box 26 loadedwith powder 24 made of a rare-earth magnetic powder for example. Thefeeder box 26 is attached with an arm 28 extending horizontally, and awiper 30 contacting the upper surface of the die 14. The arm 28 isconnected to an unillustrated electric motor or cylinder for example.Such an electric motor or cylinder slides the feeder box 26 on the uppersurface of the die 14 in left and right directions as in FIG. 1. On theother hand, the wiper 30 includes a felt 30 a and a rubber plate 30 b.The rubber plate 30 b is fixed on the felt 30 a for supporting the felt30 a. When the feeder box 26 is sliding on the upper surface of the die14, the felt 30 a wipes the powder 24 blown out of the through hole 12onto the upper surface of the die 14 as will be detailed later.

[0041] The powder 24 in the feeder box 26 contacts the upper surface ofthe die 14. When the feeder box 26 comes above the cavity 22, the powder24 in the feeder box 26 falls to fill the cavity 22. The powder 24 thusfilled in the cavity 22, is then pressed by the upper punch 16 insertedinto the through hole 12 (the cavity 22) and the lower punch 18.

[0042] As shown in FIGS. 2 and 3, the lower punch 18 is formed incorrespondence with the through hole 12 of the die 14, into a formhaving a rectangular (polyangular) section and angled portions 31. Thelower punch 18 includes a lower punch main body 32 and a lid member 34.The lid member 34 has an upper surface serving as an upper surface ofthe lower punch 18, formed with a recess 36. The recess 36 is providedwith a mirror polish for example so that a compact 72 (to be describedlater) can be separated easily from the lower punch 18. The lower punchmain body 32 has an upper surface machined into a ring portion 38. Thering portion 38 has a side surface formed with a multiplicity of throughholes as supply ports, i.e. nozzles 40. The nozzles 40 are formed inrows circumferentially as well as vertically of the ring portion 38 soas to supply a lubricant generally uniformly over the entirecircumference of a side surface of the through hole 12 of the die 14.With this arrangement, the multiplicity of the nozzles 40 capable ofspraying the lubricant to the side surface of the through hole 12 of thedie 14 from within the lower punch 18 is provided circumferentially ofthe side surface of the lower punch 18 at a portion closer to an upperend of the lower punch 18.

[0043] The lower punch 18 has an inside formed with a lubricantsupplying passage 42 communicated with each of the nozzles 40. As shownin FIG. 4, the lubricant supplying passage 42 includes a main passage 42a and sub-passages 42 b, 42 c.

[0044] The main passage 42 a includes a generally L-shaped pipe startingfrom a lower end portion of a side surface of the lower punch main body32, going inside the lower punch main body 32, making an upward turn ata center portion of the lower punch main body 32, and then going upwardto the upper surface of the lower punch main body 32.

[0045] The sub-passages 42 b, 42 c are formed in the upper surface ofthe lower punch main body 32, so as to provide a horizontal connectionbetween the main passage 42 a and each of the nozzles 40. Specifically,the sub-passages 42 b, 42 c are formed by machining the upper surface ofthe lower punch main body 32 and inside the ring portion 38, leavingfour triangular columns as guide members 44 on the upper surface of thelower punch main body 32. The sub-passage 42 b is formed in an X-shape,extending from a center portion of the upper surface of the lower punchmain body 32 toward each of the four angled portions 31. On the otherhand, the sub-passage 42 c is formed immediately inside the ring portion38 as a generally rectangular loop.

[0046] The main passage 42 a and the sub-passage 42 b guide thelubricant supplying passage 42 coming from inside the lower punch 18toward the nozzles 40 located near each of the angled portions 31.Specifically, the lubricant is first supplied to each of those nozzles40 in an adjacency to the angled portion 31, and then supplied to eachof the other nozzles 40 via the sub-passage 42 c.

[0047] A generally ring-shaped sealing member 46 is provided to encirclethe side surface of the lower punch main body 32 at a portionimmediately below each of the nozzles 40 for sealing a gap between theside surface of the lower punch 18 and the side surface of the throughhole 12 of the die 14. The sealing member 46 is made, for example, ofnitrile rubber or felt having a high sealing capability. Further, agenerally ring-shaped absorbing member 48 is provided on the uppersurface of the lower punch main body 32, surrounding the circumferenceof the ring portion 38 covering the nozzles 40. The absorbing member 48is made of a fibrous material such as felt, and therefore capable ofholding by absorption part of the lubricant applied to the side surfaceof the through hole 12 of the die 14, keeping contact with the sidesurface of the through hole 12 while being in the through hole 12.Further, the absorbing member 48 allows the lubricant to pass frominside to the outside, while functioning as a filtering member duringsuction. With the above arrangement, the side surface of the lower punch18 is provided with the sealing member 46 and the absorbing member 48.

[0048] The lid member 34, as part of the upper end portion of the lowerpunch 18, is attached on the ring portion 38 by silver-alloy brazing forexample.

[0049] The main passage 42 a of the lubricant supplying passage 42 has alower end portion (a portion extending out of the lower end portion ofthe lower punch 18) connected, via a forked member 50, to a lubricantsupplying pipe 52 and a suction pipe 54. (It should be noted here thatFIGS. 1 and 5 respectively show the lubricant supplying pipe 52 and thesuction pipe 54 in a vertical arrangement for clarity reasons, differingfrom FIGS. 2 and 3.) The lubricant supplying pipe 52 is connected to apressurizing pump 56 for sending air to the lubricant supplying passage42 whereas the suction pipe 54 is connected to a vacuum pump 58.

[0050] The supplying passage provided by the lubricant supplying pipe 52is connected with a branching pipe 60. The branching pipe 60 isconnected via a solenoid valve 62 to a tank 64 as a lubricant reservoir.The pressurizing pump 56 acts, as will be described later in moredetail, when the die 14 is moved vertically before the powder 24 isfilled in the cavity 22. While the pressurizing pump 56 is working, thesolenoid valve 62 is opened, allowing the tank 64 to drip the lubricantinto the lubricant supplying pipe 52. When the lubricant is dripped intothe air pressurized (to about 0.7 MPa) by the pressurizing pump 56, thelubricant is atomized. The atomized lubricant is carried through thelubricant supplying passage 42, and supplied through the nozzles 40 tothe side surface of the through hole 12.

[0051] It should be noted here that a solenoid valve 66 is provided inadjacency of the forked pipe 50 in the lubricant supplying pipe 52. Thesolenoid valve 66 is closed while the vacuum pump 58 is working.

[0052] On the other hand, the suction pipe 54 is provided with asolenoid valve 68 which is closed while the pressurizing pump 56 isworking, and a filter 70 located closer to the vacuum pump 58 than isthe solenoid valve 68 for preventing the vacuum pump 58 from sucking thepowder 24 or the lubricant. The vacuum pump 58 is activated, as will bedetailed later, when the cavity 22 is filled with the powder 24. Whenthe vacuum pump 58 is activated (sucking at about −0.1 MPa), the cavity22 is sucked under a reduced pressure through the absorbing member 48,the nozzles 40 and the lubricant supplying passage 42 each provided inthe lower punch 18.

[0053] As described above, the nozzles 40 also act as suction portsopened in the side surface of the lower punch 18. Thus, it has becomepossible to provide a large number of suction ports generally uniformlyaround an upper portion of the side surface of the lower punch 18.Further, the lubricant supplying passage 42 also functions as a suctionpassage through the inside of the lower punch 18 to the suction ports.Further, the absorbing member 48 also functions as a filtering membercovering the suction ports.

[0054] With the above arrangements, operation of the rare-earth magneticpowder pressing apparatus 10 will then be described with reference toFIG. 5.

[0055] A first sate shown in FIG. 5(a) is a state in which a previouscycle of the pressing operation is completed. The die 14 stays at an endof its downstroke while the upper punch 16 stays at an end of itsupstroke.

[0056] When the die 14 begins rising (See FIG. 5(b)), the pressurizingpump 56 is activated, with the solenoid valves 62 and 66 opened. On theother hand, the vacuum pump 58 stays stopped, with the solenoid valve 68stays closed. Under the above state, the lubricant is dripped from thetank 64 into the compressed air in the lubricant supplying pipe 52, andatomized in the air. The lubricant as an atomized state is suppliedthrough the lubricant supplying passage 42 of the lower punch 18 to eachof the nozzles 40. Each nozzle 40 sprays the lubricant to the sidesurface of the through hole 12 via the absorbing member 48.

[0057] During the above step, the sealing member 46 provided immediatelybelow each of the nozzles 40 in the side surface of the lower punch 18causes the lubricant and the air to be blasted upward, blowing upward toremove the powder 24 captured between the side surface of the lowerpunch 18 and the side surface of the through hole 12. This protects theside surface of the lower punch 18 and the side surface of the throughhole 12 from being damaged by the powder 24. The protection isespecially effective if the powder 24 is a highly abrasive rare-earthmagnetic powder. In addition, the lubricant applied is prevented fromfalling down by the sealing member 46.

[0058] The lubricant supplying passage 42 constituted by the mainsupplying passage 42 a and the sub-supplying passage 42 b leads the wayfrom inside the lower punch 18 to each of the nozzles 40 located nearfour angled portions 31. Therefore, the lubricant is reliably sprayedfrom the nozzles 40 located near each of the four angled portions 31,making sure that each of the four corresponding corner portions of thethrough hole 12 is applied with the lubricant reliably.

[0059] Further, part of the lubricant sprayed from the nozzles 40 isabsorbed by the absorbing member 48. When the die 14 is being moved, theabsorbing member 48 spreads the absorbed lubricant and the lubricantalready applied to the side surface of the through hole 12 for moreuniform distribution, as well as soaking up excessive amount of thelubricant. As a result, it has become possible to apply the lubricantmore uniformly while further saving the amount of lubricant applied.

[0060] Next, the die 14 begins to go down upon reaching an end of itsupstroke. Again, while the die 14 is going down (See FIG. 5(c)), thelubricant is sprayed from the nozzles 40 for application to the sidesurface of the through hole 12 in the same manner as described above. Itshould be noted here however, that if the absorbing member 48 holdsenough amount of the lubricant, it is not necessary to spray thelubricant during the downstroke of the die 14.

[0061] Next, When the die 14 reaches the end of the downstroke, thepressurizing pump 56 is deactivated and the solenoid valves 62 and 66are closed. Then, as shown in FIG. 5(d), the feeder box 26 slides towardthe through hole 12. At this time, the felt 30 a of the wiper 30 wipesthe powder 24 blown onto the upper surface of the die 14.

[0062] Then, when the feeder box 26 comes right above the through hole12, the sliding movement is stopped (See FIG. 5(e)). Next, the die 14begins rising to form the cavity 22 in an upper portion of the throughhole 12, allowing the feeder box 26 to fall the powder 24 into thecavity 22 (See FIG. 5(f)).

[0063] On the other hand, generally at the same timing as the ascensionof the die 14, the vacuum pump 58 is activated, and the solenoid valve68 is opened, so that the cavity 22 is sucked under a decreased pressurethrough the nozzles 40, the lubricant supplying passage 42, and theabsorbing member 48, by the vacuum pump 58.

[0064] During the above step, the sealing member 46 makes sure that anegative pressure necessary for the suction is reliably developed abovethe lower punch 18, increasing an effect of the sucking. Further, eachof the nozzles 40 functioning as the suction port provided at the upperportion of the lower punch 18 can decrease clogging of the powder in aregion between the side surface of the lower punch 18 and the sidesurface 12 of the through hole 12 of the die 14.

[0065] Further, the suction of the cavity 22 from each of the nozzles 40provided in the lower punch 18 makes sure that the powder 24 is reliablyfilled in each of corner portions formed by the side surface of thethrough hole 12 of the die 14 and the lower punch 18. Particularly, thesuction of the cavity 22 provided from the nozzles 40 closest to thefour angle portions 31 makes sure that the four corner portions of thethrough hole 12 respectively corresponding to the above four angleportions 31 are reliably filled with the powder 24. This advantage isespecially significant if the powder 24 contains a rare-earth magneticpowder having a poor fluidity. As a result, it becomes possible toprevent un-uniform filling of the cavity 22 with the powder 24.

[0066] Further, the absorbing member 48 functioning also as a filteringmember provides filtration so that the powder 24 does not enter insidethe lower punch 18, i.e. into the lubricant supplying passage 42. Thismakes possible to prevent clogging of the nozzles 40. Even if the powder24 is sucked in, the filter 70 provided in the suction pipe 54 reliablyprevents the powder 24 from coming into the vacuum pump 58. The filter70 also prevents the lubricant from coming into the vacuum pump 58.

[0067] Next, when the die 14 has reached its end of the upstroke, thevacuum pump 58 is deactivated. The feeder box 26 is evacuated from abovethe cavity 22 (See FIG. 5(g)). During this evacuation movement, a bottomface of the feeder box 26 wipes the powder 24 off.

[0068] Then, as shown in FIG. 5(h), the upper punch 16 comes down intothe through hole 12 (cavity 22), compressing the powder 24 within thecavity 22 with the lower punch 18 at a pressure of about 100 MPa to forma compact 72. During this formation step, the vacuum pump 58 isactivated again for sucking gases such as air (deaeration) held in abody of powder 24.

[0069] Next, upon completion of the press forming, the vacuum pump 58 isdeactivated and the solenoid valve 68 is closed. Then, the upper punch16 is raised whereas the die 14 is lowered for taking out the compact 72(See FIG. 5(i)). Since the entire side surface of the through hole 12 isapplied with a uniform coating of the lubricant, the compact 72 can betaken out smoothly and reliably.

[0070] For example, according to an experiment, a total of 50 cycles ofpress formation of the powder 24 was performed and a total of 50compacts 72 were obtained, of which none was found unfilled in anycorner portion 31, cracked or flaked.

[0071] Further, the lubricant can be applied uniformly by using even arelatively small amount of the lubricant, practically eliminatingformation of a pool of lubricant otherwise expected in the recess 36 inthe upper surface of the lower punch 18. As a result, the powder 24 iseasily compacted by the pressurization, yielding the compact 72 ofdesired characteristics. Especially, if the recess 36 is mirror polishedand even if formed to have a curved surface, the powder 24 can move inthe recess 36 under the pressure into the desired form of the compact72. Further, it becomes possible to prevent the compact 72 from beingcoated with unnecessarily large amount of lubricant. As a result, whenthe compact 72 is sintered, there will not be excess carbon, andtherefore there will not be deterioration in the magneticcharacteristics of the rare-earth magnet. Still further, life of metalmolds such as the die 14, the upper punch 16, the lower punch 18 can beincreased.

[0072] Further, prevention of un-uniform filling of the powder 24 in thecavity 22 makes possible to form the compact 72 of a good quality evenif the powder 24 is made of a rare-earth magnetic powder having a lowfluidity.

[0073] As a result, according to the above embodiment, it becomespossible to improve productivity through improved quality and yield ofthe compact 72 by the spray of atomized lubricant from each of thenozzles 40 in the side surface of the lower punch 18, and the suction ofthe cavity 22 under the reduced pressure through each of the nozzles 40while the cavity 22 is filled with the powder 24.

[0074] For example, the powder 24 may be manufactured by the followingstrip casting process. Specifically, as shown in U.S. Pat. No.5,383,978, an alloy having a composition comprising 21N-1B-68Fe (% byweight) is melted by a high-frequency melting process in an argon (Ar)gas atmosphere into a molten material. The molten material is maintainedat 1,350° C., and then thermally quenched on a single roll. Coolingconditions at this time include a roll peripheral speed of about 1 m/s,a cooling rate of 500° C./s, and a sub-cooling of 200° C. . The abovequenching-solidification process yields a body of flaky alloy having athickness of about 0.3 mm.

[0075] It should be noted here that a portion of iron (Fe) in the abovecomposition may be replaced by cobalt (Co). Further, another compositionsuch as disclosed in U.S. Pat. No. 4,770,723 by the present applicantmay also be used.

[0076] The obtained flaky alloy is allowed to absorb hydrogen forembrittlement, and then coarsely pulverized by a feather mill into flakygrains of about 5 mm. The coarsely pulverized alloy prepared by theabove process is then ground by a jet mill into alloy powder having anaverage particle size of 3.5 μm. The alloy powder is then added andmixed with a 2.0 (% by weight) of a lubricant prepared by diluting fattyacid ester with a petroleum solvent to obtain the powder 24.

[0077] The powder 24 thus prepared is then oriented in a magnetic fieldof 1.6 T, pressed under a pressure of 147 MPa into a compact 10 mm wide,10 mm high, and 20 mm long. The compact is sintered for one hour at1050° C. in an argon (Ar) gas atmosphere, aged for an hour at 600° C. inan argon (Ar) gas atmosphere to obtain a sintered magnet. The magnet hasmagnetic characteristics including, a coercive force of 1074 kA/m,residual flux density of 1.39 T, and a maximum energy product of 375kJ/m³.

[0078] The lubricant is a solvent dilution of a fatty acid ester.Specifically, the fatty acid ester may be capronic acid methyl, capricacid methyl, lauric acid methyl, lauryl acid methyl and so on.

[0079] The solvent may be a petroleum solvent represented byisoparaffin, or a naphthene solvent and so on. The fatty acid ester ismixed with the solvent at a weight ratio of 1:20 through 1:1. Inclusionof arachidic acid as a fatty acid up to 1.0 (% by weight) is acceptable.

[0080] According to the present invention, it is possible to preventun-uniform filling of the powder 24 and reduce adverse effect fromcarbon even if the powder 24 is manufactured by the above strip castingprocess, making possible to obtain a magnet having superb magneticcharacteristics.

[0081] It should be noted here that according to the above embodiment,the nozzles 40, the lubricant supplying passage 42 and the absorbingmember 48 function also as the suction ports, the suction passage andthe filtering member respectively. However, each of these functions maybe performed by a separate component. In such a case, the absorbingmember 48 may be provided at another location away from the nozzles 40.

[0082] Further, according to the above embodiment, deaeration isperformed while the powder 24 in the cavity 22 is under compression.However, this deaeration is not necessarily performed.

[0083] Still further, it is not necessary to use both methods of thelubricant applying operation and the sucking operation during the powderfilling according to the present invention. It is still possible toimprove productivity through improvement in the quality and the yield ofthe compact 72 by only using either one of the methods.

[0084] If only the lubricant application method is used (withoutperforming the suction during the powder filling,) only the lubricantsupplying pipe 52 may be connected to the lower end portion of the mainsupplying passage 42 a of the lubricant supplying passage 42, withoutthe forked member 50. In such a case, the pressing apparatus is operatedas follows for example: Specifically, as shown in FIG. 6, starting fromthe situation immediately after completion of the previous pressingcycle (See FIG. 6(a)), the die 14 is raised (See FIG. 6(b)). While thedie 14 is rising, the lubricant is sprayed from each of the nozzles 40to the side surface of the through hole 12, just in the same way as inthe above embodiment. When the die 14 has reached the end of upstroke,the die 14 is not lowered, and the feeder box 26 is slid toward thethrough hole 12 (See FIG. 6(c)). It should be noted that when the die 14has reached the end of upstroke, the cavity 22 has already been formedin the through hole 12. Next, the sliding operation is stopped when thefeeder box 26 has come right above the through hole 12, allowing thepowder 24 in the feeder box 26 to fall into the cavity 22 (See FIG.6(d)). Then, the feeder box 26 is evacuated from above the cavity 22(See FIG. 6(e)), allowing the upper punch 16 to come down, so that theupper punch 16 and the lower punch 18 can compress the powder 24 in thecavity 22 (See FIG. 6(f)). Finally, the upper punch 16 is raised whilethe die 14 is lowered so that the compact 72 can be taken out (See FIG.6(g)). According to this method therefore, a cycle speed can beincreased than that of the above embodiment.

[0085] In addition, according to the above embodiment, the lower punch18 has a rectangular section. However, the section may be anotherpolyangular shape or may be circular for application of the presentinvention. Still further, the lubricant is more likely to pool on alower punch 18 a having a deep recess 36 a as shown in FIG. 7. However,the pooling of the lubricant can be practically eliminated by the methodof lubricant application according to the present invention, makingpossible to further increase the advantages.

[0086] Further, according to the above embodiment, the lower punch 18 isfixed and the die 14 is vertically movable. However, the presentinvention is not limited by this arrangement. For example, the die 14may be fixed whereas the lower punch 18 is vertically movable.

[0087] Further, the lubricant supplying means including the nozzles andthe lubricant supplying passage and so on may be provided by using theupper punch 16. In such a case, the sealing member should seal a sidesurface of the upper punch 16 immediately above the nozzles, so that thelubricant is reliably discharged downward and the applied lubricant isprevented from leaking to the upper surface of the die for example, froma gap between the upper punch and the side surface of the through hole.

[0088] Further, the sealing member 46 may be formed integrally with thelower punch 18. The lubricant may be supplied in a form other than theatomized state as long as being supplied with a gas.

[0089] Further, the present invention is also applicable to pressing ofpowders other than the rare-earth magnetic powder such as dry pressingof a ferrite powder.

[0090] Still further, if the cavity 22 is shallow, the stroke movementof the die 14 may be stopped when the lubricant is supplied with the gasfrom the nozzles 40 to the side surface of the through hole 12 withinthe through hole 12.

[0091] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A powder pressing apparatus for formation of acompact by pressing a powder, comprising: a die having a verticalthrough hole; a first punch and a second punch, each being verticallymovable within the through hole relative to the die, for compression ofthe powder within a cavity formed in the through hole; and a supplyingmeans including a supply port provided in a side surface of the firstpunch, for supply of a lubricant with a gas from the supply port to theside surface of the through hole within the through hole.
 2. Theapparatus according to claim 1, further comprising an absorbing memberprovided in the side surface of the first punch for holding byabsorption the lubricant applied to the side surface of the through holeand for contact to the side surface of the through hole within thethrough hole.
 3. The apparatus according to claim 1, wherein: the firstpunch is formed to have a polyangular section so as to have an angledportion; the supply port being formed near the angled portion of thefirst punch; and the supplying means further including a lubricantsupplying passage connected with the supply port, through the firstpunch for supply of the lubricant to the supply port.
 4. The apparatusaccording to claim 1, further comprising a sealing portion provided inthe side surface of the first punch farther away from the cavity than isthe supply port for sealing a gap between the side surface of the firstpunch and the side surface of the through hole.
 5. The apparatusaccording to one of claims 1 through 4, wherein the first punch is alower punch.
 6. The apparatus according to claim 5, wherein the lowerpunch has an upper surface formed into a recess.
 7. The apparatusaccording to one of claims 1 through 4, wherein the powder includes arare-earth magnetic powder.
 8. The apparatus according to one of claims1 through 4, wherein: one of the first punch and the second punch is alower punch; and the apparatus further comprising a sucking means havinga suction port provided in the side surface of the lower punch, forproviding suction from the cavity under a reduced pressure from thesuction port while the cavity is being filled with the powder.
 9. Apowder pressing apparatus for formation of a compact by pressing apowder, comprising: a die having a vertical through hole; an upper punchand a lower punch, each being vertically movable within the through holerelative to the die, for compression of the powder within a cavityformed in the through hole; and a sucking means including a suction portprovided in a side surface of the lower punch, for providing suctionfrom the cavity under a reduced pressure from the suction port while thecavity is being filled with the powder.
 10. The apparatus according toclaim 9, further comprising a filtering member provided in the sidesurface of the lower punch for covering the suction port.
 11. Theapparatus according to claim 9, wherein: the lower punch is formed tohave a polyangular section so as to have an angled portion; the suctionport being formed near the angled portion of the lower punch; and thesucking means further including a suction passage connected with thesuction port, through the lower punch.
 12. The apparatus according toclaim 9, further comprising a sealing portion provided in the sidesurface of the lower punch below the suction port for sealing a gapbetween the side surface of the lower punch and a side surface of thethrough hole.
 13. The apparatus according to one of claims 9 through 12,wherein the powder includes a rare-earth magnetic powder.
 14. A methodof pressing a powder for formation of a compact through compression ofthe powder by a first punch and a second punch within a cavity formed ina vertical through hole of a die, comprising: a lubricant supplying stepof supplying a lubricant with a gas from a side surface of the firstpunch to a side surface of the through hole within the through hole; apowder filling step of filling the cavity with the powder; and a pressforming step of forming the compact by pressing the powder filled in thecavity by the first punch and the second punch.
 15. The method accordingto claim 14, further comprising a step of spreading the lubricantapplied to the side surface of the through hole.
 16. The methodaccording to claim 14, wherein: the first punch is formed to have apolyangular section so as to have an angled portion; and the lubricantbeing supplied from inside the first punch through near the angledportion to the side surface of the through hole in the lubricantsupplying step.
 17. The method according to claim 14, wherein: a gapbetween the side surface of the first punch and the side surface of thethrough hole is sealed while the lubricant is supplied to the sidesurface of the through hole in the lubricant supplying step.
 18. Themethod according to one of claims 14 through 17, wherein the first punchis a lower punch.
 19. The method according to claim 18, wherein thelower punch has an upper surface formed into a recess.
 20. The methodaccording to one of claims 14 through 17, wherein the powder includes arare-earth magnetic powder.
 21. The method according to one of claims 14through 17, wherein: one of the first punch and the second punch is alower punch; and the cavity being under suction by a reduced pressureprovided from the side surface of the lower punch while the powder isbeing filled into the cavity in the powder filling step.
 22. A method ofpressing a powder for formation of a compact through compression of thepowder by an upper punch and a lower punch within a cavity formed in avertical through hole of a die, comprising: a powder filling step offilling the cavity with the powder while the cavity is under suction bya reduced pressure provided from a side surface of the lower punch; anda press forming step of forming the compact by pressing the powderfilled in the cavity by the upper punch and the lower punch.
 23. Themethod according to claim 22, wherein filtration is provided during thesuction from the cavity by the reduced pressure for preventing the lowerpunch from sucking the powder in the powder filling step.
 24. The methodaccording to claim 22, wherein the lower punch is formed to have apolyangular portion so as to have an angled portion; and the cavitybeing under suction by a reduced pressure provided from near the angledportion in the powder filling step.
 25. The method according to claim22, wherein a gap between the side surface of the lower punch and a sidesurface of the through hole is sealed while the cavity is under thesuction by the reduced pressure in the powder filling step.
 26. Themethod according to one of claims 22 through 25, wherein the powderincludes a rare-earth magnetic powder.
 27. The method according toclaims 26, wherein the rare-earth magnetic powder is manufactured by astrip casting process.
 28. A powder pressing apparatus for formation ofa compact by pressing a powder, comprising: a die having a verticalthrough hole; a first punch and a second punch, each being verticallymovable within the through hole relative to the die, for compression ofthe powder within a cavity formed in the through hole; a lubricantholding means provided in a side surface of the first punch, forapplication of a lubricant to a side surface of the through hole incontact with the side surface of the through hole,; and a lubricantsupplying means for supply of the lubricant to the lubricant holdingmeans.
 29. The apparatus according to claim 28, wherein the powderincludes a rare-earth magnetic powder.
 30. A method of pressing a powderfor formation of a compact through compression of the powder by a firstpunch and a second punch within a cavity formed in a vertical throughhole of a die, comprising: a lubricant supplying step of supplying alubricant to a side surface of the through hole by bringing a lubricantholding means holding the lubricant into contact with the side surfaceof the through hole; a powder filling step of filling the cavity withthe powder; and a press forming step of forming the compact by pressingthe powder filled in the cavity by the first punch and the second punch.31. The method according to claim 30, wherein the powder includes arare-earth magnetic powder.